1. Technical Field
The present invention relates to a calibration method and system, and a delay time calculation method thereof. More particularly, the present invention relates to a method and system for calibrating time synchronization between image taking and coordinate reading, and a delay time calculation method thereof, which are applied in the surgical navigation.
2. Description of Related Art
FIG. 1 shows an existing hardware arrangement for surgical navigation. In the surgical navigation hardware arrangement 10 of FIG. 1, dynamic reference frames (DRFs) 14a, 14b, and 14c are respectively provided on a surgical instrument 11, at a surgical site 12, and on a calibrator 13 mounted at the receiving end of an image taking device 17. Signals transmitted from an optical positioning device 15 are reflected by the DRFs 14a, 14b, and 14c and received by the optical positioning device 15. The surgical navigation system 16 receives the DRF coordinates of the calibrator 13 and of the surgical site 12 from the optical positioning device 15. Accompanying with the image of the calibrator 13 and the surgical site 12 taken by the image taking device 17 and the DRF coordinates, the surgical navigation system 16 calculates the relationship between the DRF coordinates and the image coordinates. Finally, the surgical site 12 and the dynamic position of the surgical instrument 11 can be displayed at the corresponding positions in the image to provide surgeons the desired surgical navigation information.
The surgical navigation system 16 depends heavily on a precise coordinate correspondence relationship. That is to say, the DRF coordinates must correspond precisely to the image coordinates, or the navigation information provided by the surgical navigation system 16 will be imprecise. However, even if the coordinates of the DRFs 14a, 14b, and 14c detected by the optical positioning device 15 are received by the surgical navigation system 16 immediately after the image taken by the image taking device 17 is received, there is always a time difference between the taking of the image and the reading of the DRF coordinates. Should the patient being operated on move during such a time difference, the DRF coordinates obtained will not correspond correctly to the image received; as a result, the navigation information becomes imprecise. Therefore, a method and system for calibrating the time difference between image taking and DRF coordinate reading is needed. It is desirable that the time difference only has to be calculated once for the same surgical navigation hardware arrangement 10 and can be used in all subsequent surgical navigation calibrations. It is also desirable that the surgical navigation system 16 is readily applicable to different surgical navigation hardware arrangements 10.